The present invention relates to medical electrical leads generally and more particularly to implantable defibrillation electrodes and leads.
For some time, it has been recognized that in the context of implantable cardioverters and defibrillators, an electrode system employing transvenous leads alone or combination with subcutaneous electrodes provides substantial advantages as compared to epicardial electrode systems. In this context, use of a defibrillation electrode located in the right ventricle is conventional. In such leads, the defibrillation electrode typically takes the form of an elongated coil, mounted exterior to the insulative body of the lead.
In electrode systems presently under clinical evaluation, and presently for sale commercially outside the United States, right ventricular defibrillation leads typically also include one or more electrodes for cardiac pacing and sensing. It has been recognized for some time that the use of a bipolar electrode pair, mounted to such a right ventricular defibrillation lead is desirable. For example, U.S. Pat. No. 5,044,375 issued to Bach et al. discloses such a lead, as does U.S. Pat. No. 5,050,601 issued to Kupersmith and U.S. Pat. No. 5,144,960 issued to Mehra.
Like cardiac pacing leads, implantable defibrillation leads benefit from the inclusion of fixation apparatus. Passive fixation apparatus, such tines, are disclosed for example in the above cited Bach reference. Active fixation devices, such as metal helixes which are screwed into the heart tissue, are disclosed in the above-cited Kupersmith and Mehra et al. patents. In the right ventricular defibrillation leads presently manufactured and sold by Medtronic, two electrodes are provided for pacing and sensing, one taking the form of an advanceable helical electrode as generally disclosed in U.S. Pat. No. 4,106,512 issued to Bisping, the second electrode taking the form of a ring electrode. Both the helical electrode and the ring electrode are mounted distal to an elongated defibrillation electrode.
Generally, in order to accomplish reliable sensing of ventricular depolarizations employing a bipolar electrode pair, an intra-electrode spacing of 5 mm or more is generally believed desirable. In addition, some degree of spacing between the sensing electrodes and the right defibrillation electrode is also believed desirable. These constraints, taken together, have typically resulted in practical defibrillation lead designs in which the distal end of the defibrillation electrode is substantially spaced from the distal end of the lead body.
The present invention is directed towards optimizing the size, spacing and location of the electrodes on a defibrillation lead of the type including an elongated defibrillation electrode and two electrodes used for sensing of cardiac depolarizations. In particular, the invention is directed toward providing a bipolar sensing pair of electrodes having adequate interelectrode spacing to assure appropriate sensing of cardiac depolarizations, while still allowing placement of the defibrillation electrode as close to the distal end of the lead body as possible.
The present invention accomplishes these desired results by employing an electrode set comprising a helical electrode, extending distally from the lead body, for use as the active electrode in cardiac pacing and for use in sensing cardiac depolarizations. A ring tip electrode or a cylindrical ring electrode is located at or adjacent to the distal end of the lead body, and provides the second electrode for use in sensing depolarizations. The helical electrode is insulated from the point it exits the lead body until a point adjacent its distal end, thereby spacing the effective electrode surface of helical electrode about one-half centimeter or greater from the ring electrode. The defibrillation electrode is mounted with its distal end closely adjacent the distal end of the lead body as well, such that its distal end point is within one centimeter of the distal end of the lead body, which is made possible by the configuration of the ring and helical electrodes, as discussed above.
While the individual piece parts necessary to assemble the present invention may be found in individual prior art references, their combination, as discussed above, provides the synergistic result of a defibrillation lead having the distal end of its defibrillation electrode closely spaced to the end of the lead body, while retaining a bipolar electrode pair for sense which has adequate interelectrode separation.